How to check the float variable contain Real Numbers or not in c++?

Question

How to check the float variable contain Real Numbers or not in C++ ?

ex: -1.#IND000 my value

How to determine whether it is Real numbers or like above numbers .

Possible duplicate of: [http://stackoverflow.com/questions/570669/checking-if-a-double-or-float-is-nan-in-c] (Checking if a double or float is nan in C++) — Stephen Quan, May 09 '13 at 06:41
Stephen's link's good - though you have to dig a little: numbers can be +/- infinite as well as NaN: you can use e.g. isfinite() from boost: http://www.boost.org/doc/libs/1_38_0/libs/math/doc/sf_and_dist/html/math_toolkit/special/fpclass.html — Tony Delroy, May 09 '13 at 06:51

score 2 · Answer 1 · answered May 09 '13 at 06:33

2

converting into bool (explicitly o by mean of whatever logical operator) will give "false" for all values that are not "real" or that are 0, so

bool is_number(double d)
{ return d || d==0; }

should be fine.

answered May 09 '13 at 06:33

Emilio Garavaglia

score 2 · Accepted Answer · answered May 09 '13 at 06:34

2

There are functions like std::isnan in header <cmath>.

answered May 09 '13 at 06:34

There is no isnan() function available in current C++ Standard Library now – Pixel May 09 '13 at 06:43
@HitMe The *current* C++ standard library is C++11. If your compiler doesn't support C++11 yet, there's `isnan` in `` as of C99. If your compiler doesn't even support that, consider upgrading it. – Angew is no longer proud of SO May 09 '13 at 06:52
It's specified in C++11 26.8.3. – Tony Delroy May 09 '13 at 06:52

score 1 · Answer 3 · edited May 23 '17 at 12:24

1

These following returns true if it's a number, false otherwise:

bool test1(double d) { return d == d; }
bool test2(double d) { return d * 0.0 == 0.0; }

edited May 23 '17 at 12:24

Community

answered May 09 '13 at 06:52

Stephen Quan

Shishir Gupta · Answer 4 · 2013-07-02T11:20:31.067

1

A very simple way..

float a=3.9;
long b;
b=a;
if ((float)b==a)
    cout<<"Non-real, i.e. integer";
else
    cout<<"REAL";

edited Jul 02 '13 at 11:20

answered May 09 '13 at 07:01

Shishir Gupta

ALM865 · Answer 5 · 2014-10-07T03:14:34.350

1

You can use '_isnan' in Visual Studio (it is included in float.h):

float T;

T=std::numeric_limits<double>::quiet_NaN(); //YOUR CALCS HERE!!

if (_isnan(T)) {
    printf("error\n");
}

edited Oct 07 '14 at 03:14

answered Oct 07 '14 at 01:23

ALM865

5 Answers5